In the book Scorecasting (great book), they talk about the value of blocks, meaning that some NBA shotblockers are better than others when it comes to the quality of blocks. The researchers assigned values to the blocks (e.g., 1 for a block to yourself, 0.5 for a block that goes out of bounds to the other team, etc). It ended up that Dwight was one of the "worst" shotblockers when it comes to value (with Duncan often near the top).
I had a lot of issues with their argument (e.g., doesn't take into account the value fo intimidation, altered shots, etc, which they readily admit), but I thought it was interesting. Some of the worst shot blockers by value including Dwight, Dampier, and Dalembert.